1. Field of the Invention
This application relates to printing of hard copy i.e., human readable, characters to the high quality printing standards required for automatic optical or other reading of such characters. (As used herein, the term "automatic reading" is intended to include not only readers in which the document is fed through the reader, but also hand held wand-type readers which are manually drawn across the document.) More particularly, it relates to the printing of such characters on conventional paper stock, such as is used for tags and labels, and especially in machines of the type where the printing action is of the squeeze, low impact type rather than the high kinetic energy, high impact type as occurs for example in a typewriter.
In the former, i.e., squeeze, type of printing when done on conventional paper stock, it has been found difficult to obtain the high quality, very accurate printing needed for automatic reading of the characters.
The present invention relates to printing such high quality automatically readable characters on paper tag and label stock by a heat responsive ink material, for example an ink ribbon of the hot foil stamp type.
2. Description of the Prior Art
The hot stamp printing technique using a foil ribbon is exemplified by the following U.S. Pat. Nos. 3,022,724; 3,097,592; 3,244,092; 3,301,370; and 3,430,557. However, such prior art devices employ hot stamp printing for an entirely different purpose and in an entirely different environment from the present invention. As indicated in these patents, they are for the typical purpose of printing on very smooth, glossy, non-fibrous, plastic surfaces, one example being for printing on a smooth plastic film. Because of the glossy and non-porous nature of such materials, it is extremely difficult to print on them. They are essentially non-wettable by and non-adhesive with usual printing inks. The hot stamp technique is one of the few practical ways of printing conventional information on such surfaces. The hot stamp technique is also used for printing on extremely rough surfaces such as fabric; and where special decorative effects such as metallic printing are desired.
U.S. Pat. No. 2,351,073 discloses a carbon paper which is non-smudging at ambient temperatures. In use, the carbon paper is fed around the typewriter platen, and is heated just before it arrives at the platen. While still hot, it is operated on by the type bars, and then subsequently cools back to its normal ambient non-smudging state.
U.S. Pat. No. 3,726,212 relates to thermally printing a non-smudging, three-color bar code representative of a character, but not the character itself.